U.S. patent application number 13/678993 was filed with the patent office on 2014-05-22 for line isolation of radio frequency devices.
This patent application is currently assigned to RAYTHEON COMPANY. The applicant listed for this patent is RAYTHEON COMPANY. Invention is credited to Andrew K. Brown, Shane A. O'Connor.
Application Number | 20140139300 13/678993 |
Document ID | / |
Family ID | 50727395 |
Filed Date | 2014-05-22 |
United States Patent
Application |
20140139300 |
Kind Code |
A1 |
Brown; Andrew K. ; et
al. |
May 22, 2014 |
Line Isolation of Radio Frequency Devices
Abstract
A radio frequency (RF) device includes a transmission line
arranged on a substrate, the transmission line operative to
propagate an RF signal having a wavelength (.lamda.), and a first
isolation portion arranged on the substrate proximate to the
transmission line, the first isolation portion including an
arrangement of stubs, where each stub of the arrangement of stubs
has a length (y) where y=1/4.lamda., the first isolation portion
operative to substantially prevent electromagnetic interference
caused by the propagation of the RF signal in the transmission line
from passing through the first isolation portion.
Inventors: |
Brown; Andrew K.; (Hesperia,
CA) ; O'Connor; Shane A.; (Rancho Cucamonga,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RAYTHEON COMPANY |
Waltham |
MA |
US |
|
|
Assignee: |
RAYTHEON COMPANY
Waltham
MA
|
Family ID: |
50727395 |
Appl. No.: |
13/678993 |
Filed: |
November 16, 2012 |
Current U.S.
Class: |
333/246 ; 216/13;
427/58 |
Current CPC
Class: |
H01P 11/002 20130101;
H05K 1/0216 20130101; H01P 1/20363 20130101; H01P 3/081
20130101 |
Class at
Publication: |
333/246 ; 427/58;
216/13 |
International
Class: |
H01P 3/08 20060101
H01P003/08 |
Claims
1. A radio frequency (RF) device comprising: a transmission line
arranged on a substrate, the transmission line operative to
propagate an RF signal having a wavelength (.lamda.); and a first
isolation portion arranged on the substrate proximate to the
transmission line, the first isolation portion including an
arrangement of stubs, where each stub of the arrangement of stubs
has a length (y) where y=1/4.lamda., the first isolation portion
operative to substantially prevent electromagnetic interference
caused by the propagation of the RF signal in the transmission line
from passing through the first isolation portion.
2. The device of claim 1, wherein the transmission line includes a
conductive material.
3. The device of claim 1, wherein each stub of the arrangement of
stubs includes a conductive material.
4. The device of claim 1, wherein the first isolation portion
includes a body portion arranged on the substrate proximate to the
transmission line.
5. The device of claim 4, wherein the arrangement of stubs extends
outwardly from the body portion.
6. The device of claim 4, wherein the body portion includes a
conductive material.
7. The device of claim 1, wherein each stub of the arrangement of
stubs includes a rectangular shape.
8. The device of claim 1, wherein each stub of the arrangement of
stubs is arranged with a longitudinal axis that intersects a line
tangential to an edge of the transmission line at a substantially
90 degree angle.
9. The device of claim 1, wherein each stub of the arrangement of
stubs is arranged with a longitudinal axis that intersects a line
tangential to an edge of the transmission line at an oblique
angle.
10. The device of claim 1, further comprising a second isolation
portion including an arrangement of stubs, where each stub of the
arrangement of stubs has a length (y) where y=1/4.lamda., arranged
on the substrate proximate to the transmission line.
11. The device of claim 1, further comprising an arrangement of
conductive vias passing through the substrate proximate to the
transmission line, wherein each via of the arrangement of vias is
spaced from an adjacent via a distance operative to prevent
electromagnetic interference from passing through the arrangement
of vias.
12. A radio frequency (RF) device comprising: a transmission line
arranged on a substrate, the transmission line operative to
propagate an RF signal having a wavelength (.lamda.); a first
isolation portion arranged on the substrate proximate to the
transmission line, the first isolation portion including an
arrangement of stubs, where each stub of the arrangement of stubs
has a length (y) where y=1/4.lamda., the first isolation portion
operative to substantially prevent electromagnetic interference
caused by the propagation of the RF signal in the transmission line
from passing through the first isolation portion; and a capping
layer disposed over the substrate, the transmission line, and the
first isolation portion.
13. The RF device of claim 12, further comprising a first
conductive layer disposed on a portion of the capping layer, and a
second conductive layer disposed on an opposing surface of the
substrate.
14. The RF device of claim 13, further comprising an arrangement of
conductive vias electrically connected to the first conductive
layer and the second conductive layer, each conductive via of the
arrangement of conductive vias passes through the capping layer and
the substrate.
15. The RF device of claim 14, wherein the vias are electrically
connected to ground.
16. The RF device of claim 14, wherein each via of the arrangement
of vias is spaced from an adjacent via a distance operative to
prevent electromagnetic interference from passing through the
arrangement of vias.
17. A method for fabricating a radio frequency (RF) device, the
method comprising: determining a wavelength (.lamda.) of an RF
signal that will propagate through a transmission line; calculating
a length (y) of a stub portion of an isolator portion where
y=1/4.lamda.; depositing a layer of conductive material on a
substrate; patterning the layer of conductive material to form the
transmission line and an isolator portion comprising a plurality of
the stub portions arranged proximate to the transmission line;
depositing a capping layer on exposed portions of the substrate,
the transmission line, and the isolator portion.
18. The method of claim 17, further comprising: etching to remove
portions of the capping layer and the substrate to define a
plurality of cavities communicative with a surface of the capping
layer and an opposing surface of the substrate; depositing a first
conductive layer on the opposing surface of the substrate; and
depositing a second conductive layer on the capping layer in the
plurality of cavities to fill the plurality of cavities.
19. The method of claim 18, wherein the filled plurality of
cavities defines an arrangement of conductive vias passing through
the substrate proximate to the transmission line, wherein each via
of the arrangement of vias is spaced from an adjacent via a
distance operative to prevent electromagnetic interference from
passing through the arrangement of vias.
20. The method of claim 17, wherein the isolation portion is
operative to substantially prevent electromagnetic interference
caused by the propagation of the RF signal in the transmission line
from passing through the isolation portion.
Description
BACKGROUND
[0001] The present disclosure relates to radio frequency devices,
and more specifically, to apparatus and methods for isolating
transmission lines in radio frequency (RF) devices.
[0002] Radio frequency devices may include one or more transmission
lines arranged on a substrate that are operative to propagate RF
signals. The RF signals may cause interference in the devices if
the transmission lines are not properly isolated from other
transmission lines, integrated circuitry, or other features
arranged on the substrate.
[0003] FIG. 1 illustrates top view partially cut-away view of a
prior art example of a portion of an RF device arranged on a
substrate 100. The illustrated example includes transmission lines
102 arranged on the substrate 100. The transmission lines 102
include a conductive material, and are operative to transmit RF
signals as indicated by the arrows 101. A plurality of conductive
vias 104 that are connected to ground is arranged between the
transmission lines 102. The conductive vias 104 are sized and
spaced such that RF signals in a particular range of frequencies do
not pass through the arrangement of conductive vias 104. The
spatial distance (a) between the conductive vias 104 is partially
dependent on the frequency of the propagated RF signals. In this
regard, a device designed to propagate a higher frequency RF signal
would have more conductive vias 104 spaced at a smaller distance
than a device designed to propagate a relatively lower frequency RF
signal.
[0004] FIG. 2 illustrates a side cut-away view of the prior art
example along the line 2 of FIG. 1. Referring to FIG. 2, the
transmission lines 102 are disposed on the substrate 100 that
include a dielectric material. The transmission lines 102 are
capped with a capping layer 202 that includes an insulator
material. A first conductive layer 204 is arranged on the capping
layer 202 and a second conductive layer 206 is arranged on an
opposing surface of the substrate 100. The conductive via 104 is
communicative through the substrate 100 and the capping layer and
is electrically connected to the first conductive layer 204 and the
second conductive layer 206. The first conductive layer 204 and the
second conductive layer 206 are connected to ground such that the
conductive vias 104 are grounded.
SUMMARY
[0005] According to one embodiment of the present invention, a
radio frequency (RF) device includes a transmission line arranged
on a substrate, the transmission line operative to propagate an RF
signal having a wavelength (.lamda.), and a first isolation portion
arranged on the substrate proximate to the transmission line, the
first isolation portion including an arrangement of stubs, where
each stub of the arrangement of stubs has a length (y) where
y=1/4.lamda., the first isolation portion operative to
substantially prevent electromagnetic interference caused by the
propagation of the RF signal in the transmission line from passing
through the first isolation portion.
[0006] According to another embodiment of the present invention, a
radio frequency (RF) device includes a transmission line arranged
on a substrate, the transmission line operative to propagate an RF
signal having a wavelength (.lamda.), a first isolation portion
arranged on the substrate proximate to the transmission line, the
first isolation portion including an arrangement of stubs, where
each stub of the arrangement of stubs has a length (y) where
y=1/4.lamda., the first isolation portion operative to
substantially prevent electromagnetic interference caused by the
propagation of the RF signal in the transmission line from passing
through the first isolation portion, and a capping layer disposed
over the substrate, the transmission line, and the first isolation
portion.
[0007] According to yet another embodiment of the present
invention, a method for fabricating a radio frequency (RF) device
includes determining a wavelength (.lamda.) of an RF signal that
will propagate through a transmission line, calculating a length
(y) of a stub portion of an isolator portion where y=1/4.lamda.,
depositing a layer of conductive material on a substrate,
patterning the layer of conductive material to form the
transmission line and an isolator portion comprising a plurality of
the stub portions arranged proximate to the transmission line,
depositing a capping layer on exposed portions of the substrate,
the transmission line, and the isolator portion.
[0008] Additional features and advantages are realized through the
techniques of the present embodiments. Other embodiments and
aspects of the embodiments are described in detail herein and are
considered a part of the claimed embodiments. For a better
understanding of the embodiments with the advantages and the
features, refer to the description and to the drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] The subject matter which is regarded as the embodiments is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The forgoing and other
features, and advantages of the embodiments are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0010] FIG. 1 illustrates top view partially cut-away view of a
prior art example of a portion of an RF device arranged on a
substrate.
[0011] FIG. 2 illustrates a side cut-away view of the prior art
example along the line 2 of FIG. 1.
[0012] FIG. 3 illustrates an exemplary embodiment of a portion of
an RF device.
[0013] FIG. 4 illustrates a side cut-away view of the device along
the line 4 of FIG. 3.
[0014] FIG. 5 illustrates an alternate exemplary embodiment of a
portion of an RF device.
[0015] FIG. 6 illustrates a side cut-away view of the device 500
along the line 6 of FIG. 5.
[0016] FIG. 7 illustrates another alternate exemplary embodiment of
an RF device.
[0017] FIG. 8 illustrates another alternate exemplary embodiment of
an RF device.
[0018] FIG. 9 illustrates another alternate exemplary embodiment of
an RF device.
[0019] FIG. 10 illustrates a graphical representation of simulated
test results of a prior art arrangement similar to the arrangement
in FIG. 1.
[0020] FIG. 11 illustrates a graphical representation of simulated
test results of an arrangement similar to the arrangement in FIG.
5.
DETAILED DESCRIPTION
[0021] As discussed in reference to the prior art FIGS. 1 and 2
above, the conductive vias 104 pass through the substrate 100. The
conductive vias 104 are formed by removing material completely
through the substrate 100, thereby reducing the mechanical
integrity of the substrate. As discussed above, if the frequency of
the transmitted RF signals is increased, the spacing of the
conductive vias 104 is reduced. Since each conductive via 104
adversely impacts the integrity of the substrate 100, if too many
conductive vias are arranged in close proximity to each other, the
substrate may be easily broken due to a lack of sufficient
substrate material disposed between adjacent conductive vias 104.
Thus, relying on the use of conductive vias 104 to isolate the RF
transmission lines from proximate features arranged on the
substrate becomes problematic due to the resultant tight spacing of
the conductive vias 104 when the frequencies of the propagated RF
signals are relatively high.
[0022] FIG. 3 illustrates an exemplary embodiment of a portion of
an RF device 300 that includes an RF transmission line 302 arranged
on a substrate 304. The device 300 includes RF isolator portions
306 arranged proximate to and on opposing sides of the RF
transmission line 302. Substrate 304 includes, for example, a
dielectric material. The RF transmission line 302 includes a
conductive material such as, for example, copper, gold, or aluminum
patterned on the substrate 304. The RF isolator portions 306
include a conductive material patterned on the substrate 304 and
may include a similar or material as the RF transmission line 302.
The device 300 also includes an arrangement of conductive vias 312.
The conductive vias 312 are connected to ground and provide RF
isolation of the RF interference from emanating from the RF
transmission line 302.
[0023] The RF isolator portions 306 include an arrangement of stubs
308 extending from a body portion 310 arranged proximate to the RF
transmission line 302. Each of the stubs 308 has a length (y) and a
width (w), and are spaced at a distance (z). The dimensions of the
stubs 308 are determined during the design of the device 300. In
this regard, the wavelength (.lamda.) of the RF signal propagating
in the RF transmission line 302 indicated by the line 301 is used
to determine the length of the stubs 308, which are 1/4.lamda.,
thus y=1/4.lamda.. The spacing distance z is greater than the width
w, but is less than 1/4.lamda.. The stubs 308 are operative to
receive and propagate RF interference from the RF signal
propagating in the RF transmission line 302 the distal end 303 of
the stubs 308 is operative to reflect the RF interference. The
1/4.lamda. length of the stubs results in an apparent short in the
impedance of the stubs 308 in the opposing distal end 305. The
apparent short effectively prevents RF interference from emanating
from the RF transmission line 302 past the isolator portion 306
(for RF signals having a wavelength .lamda. and stubs 308 having a
length 1/4.lamda.). In this regard,
.lamda. = c f ( e ) ; ##EQU00001##
where C is the speed of light (3.times.10.sup.8 m/s), f is the
frequency in Hz. .di-elect cons..sub.e is determined by the
transmission line architecture for example, a microstrip
transmission line architecture (i.e. no capping layer) is defined
as follows:
when ( W H ) < 1 ; ##EQU00002## e = r + 1 2 + r - 1 2 [ ( 1 + 12
( H W ) ) - 1 2 + .004 ( 1 - ( W H ) ) 2 ] ; ##EQU00002.2## when (
W H ) .gtoreq. 1 ; ##EQU00002.3## e = r + 1 2 + r - 1 2 ( 1 + 12 (
H W ) ) - 1 2 ; ##EQU00002.4##
where W is the width of the stub 308, H is the height of the
substrate 304; .di-elect cons..sub.e is the effective permittivity
and .di-elect cons..sub.r is the relative permeability.
[0024] In some exemplary embodiments a capping layer having a
similar geometry and dielectric constant as the substrate 304 may
be used. The effective permittivity in such embodiments is equal to
the relative permittivity of the substrate. In this regard,
.di-elect cons..sub.e=.di-elect cons..sub.r.
[0025] FIG. 4 illustrates a side cut-away view of the device 300
along the line 4 (of FIG. 3). FIG. 4 illustrates the arrangement of
the isolator portions 306 having the stubs 308 and the RF
transmission line 302 on the substrate 304. A capping layer 402 may
be arranged over the substrate 304 and isolator portions 306. The
capping layer 402 may include, for example, an insulator material
such as, an oxide or nitride material a substrate, or, in some
exemplary embodiments, the capping layer 402 may include air (i.e.,
no capping layer).
[0026] FIG. 5 illustrates an alternate exemplary embodiment of a
portion of an RF device 500. The device 500 includes isolator
portions 306 arranged on a substrate 304. The device 500 also
includes an arrangement of conductive vias 502. The conductive vias
502 are connected to ground and provide RF isolation of the RF
interference from emanating from the RF transmission line 302. The
distance (b) between the conductive vias 502 may be selected to
provide RF isolation of lower wavelength interference that may
emanate from the RF transmission line 302. In this regard, the
conductive vias 502 may be sized and arranged to provide RF
isolation for a range of particular RF interference emanating from
the RF transmission line 302, while the isolator portions 306 may
be sized, shaped, and arranged to provide RF isolation for another
range of particular RF interference emanating from the RF
transmission line 302. Thus, the combination of the isolator
portions 306 and the conductive vias 502 may be used in combination
to effectively isolate a broad range of RF interference emanating
from the RF transmission line 302.
[0027] FIG. 6 illustrates a side cut-away view of the device 500
along the line 6 (of FIG. 5). The device 500 includes a capping
layer 404, a first conductive layer 602 arranged on the capping
layer 404, and a second conductive layer 604 arranged on the
opposing surface of the substrate 304. The first conductive layer
602 and the second conductive layer 604 are connected to ground and
the conductive vias 502 such that the conductive vias 502 are
grounded.
[0028] The exemplary embodiment illustrated in FIGS. 5 and 6 may be
fabricated by any number of exemplary methods. For example, once
the wavelength .lamda. of the RF signal that will be propagated
through the RF transmission line 302 is determined, the spacing and
size of the conductive vias 502 may be defined. The lengths of the
stubs 308 are defined as 1/4.lamda.. Once the dimensions and layout
of the device 500 is determined, a layer of conductive material may
be deposited on the substrate 302 and patterned using, for example,
a photolithographic etching process to define the RF transmission
line 302 and the isolator portions 306. The capping layer 404 is
deposited over the exposed portions of the substrate 304, the RF
transmission line 302, and the isolator portions 306 using, for
example, an oxidation process, a chemical vapor deposition (CVD) or
a plasma enhanced chemical vapor deposition process (PECVD). The
vias 502 may be formed by, for example, performing a
photolithographic patterning and etching process that removes
exposed portions of the capping layer 402 and the substrate 304 to
form cavities that are communicative between the capping layer 402
and the substrate 304. The first conductive layer 602 is deposited
on the capping layer 404 using for example, suitable deposition
process such as, for example, a spin coating process, CVD, PEDVC.
Other fabrication methods may include, for example, a screen
printing process to apply traces, or a laser ablation process to
remove conductive material from undesired regions. The cavities
defining the conductive vias 502 may be filled with the conductive
material deposited, for example during the deposition of the first
conductive layer 602. The second conductive layer 604 may be
deposited on the opposing surface of the substrate 602 using a
suitable deposition process. The use of conductive vias 502 with
the stubs 308 allows provides for isolation of higher frequency RF
interference (isolated by the stubs 308) and lower frequency RF
interference (isolated by the conductive vias 502) without spacing
the conductive vias 502 in a manner that reduces the structural
integrity of the substrate 304 close to the point of structural
failure.
[0029] FIG. 7 illustrates another alternate exemplary embodiment of
an RF device 700. In the illustrated embodiment, isolator portions
706 include stubs 308 arranged at an oblique angle (.phi.) relative
to the body portion 310. In this regard, the lengths of the stubs
308 are measured along the centerlines of the stubs 308.
[0030] FIG. 8 illustrates another alternate exemplary embodiment of
an RF device 800. In the illustrated embodiment, isolator portions
806 do not include a body portion, but rather a plurality of stubs
308 that affect the isolation of the RF signals in a similar manner
as described above. In the illustrated embodiment, each of the
stubs 308 are arranged at a substantially 90 degree angle relative
to a line 801 that defines the path of the transmission line 302.
Though the illustrated embodiment includes a transmission line 302
that is substantially straight, alternate embodiments may include a
curved transmission line 302. In such embodiments, the stubs 308
may include a linear axis that intersects a line tangential to an
edge of the transmission line 302 at a substantially 90 degree
angle or at an oblique angle as shown above for example, in FIG.
7.
[0031] FIG. 9 illustrates another alternate exemplary embodiment of
an RF device 900. The device 900 is similar to the embodiments
described above, however the isolator portion 906 includes stubs
908 having curved profiles 901. The length of the stubs 908 (i.e.,
1/4 .lamda.) is distributed along the line 903 that corresponds to
the curved profiles 901.
[0032] The exemplary embodiments of the isolator portions described
above in FIGS. 7, 8, and 9 may be arranged at any suitable angle
relative to a body portion 310 and may have any curved or arcuate
profiles. The embodiments may or may not include a body portion 310
or portions of a body portion 310. The embodiments may or may not
include conductive vias as described above depending on design
specifications.
[0033] FIG. 10 illustrates a graphical representation of simulated
test results of a prior art arrangement similar to the arrangement
described above in FIG. 1. FIG. 10 includes a graphical
representation of electromagnetic interference represented by the
shaded regions, where the undesirable electromagnetic interference
passes through the arrangements of conductive vias 104. As
discussed above, though reducing the spacing between the conductive
vias 104 (and increasing the number of conductive vias 104) may
reduce the undesirable electromagnetic interference that passes
through the arrangements of conductive vias 104, reducing the
spacing may not be practical if the reduction in spacing and the
addition of more conductive vias 104 structurally weakens the
substrate.
[0034] FIG. 11 illustrates a graphical representation of simulated
test results of an arrangement similar to the arrangement described
above in FIG. 5. In the illustrated test results, the
electromagnetic interference does not pass through the isolator
portions 306, thus effectively isolating the RF transmission lines
302, where the electromagnetic interference is illustrated by
shaded regions that do not pass through the isolator portions
306.
[0035] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the embodiments. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one more other features, integers,
steps, operations, element components, and/or groups thereof.
[0036] The corresponding structures, materials, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material, or
act for performing the function in combination with other claimed
elements as specifically claimed. The description of the present
embodiments has been presented for purposes of illustration and
description, but is not intended to be exhaustive or limited to the
embodiments in the form disclosed. Many modifications and
variations will be apparent to those of ordinary skill in the art
without departing from the scope and spirit of the embodiments. The
embodiment was chosen and described in order to best explain the
principles of the embodiments and the practical application, and to
enable others of ordinary skill in the art to understand the
embodiments for various embodiments with various modifications as
are suited to the particular use contemplated.
[0037] The diagrams depicted herein are just one example. There may
be many variations to this diagram or the steps (or operations)
described therein without departing from the spirit of the
embodiments. For instance, the steps may be performed in a
differing order or steps may be added, deleted or modified. All of
these variations are considered a part of the claimed
embodiments.
[0038] While the preferred embodiment to the embodiments had been
described, it will be understood that those skilled in the art,
both now and in the future, may make various improvements and
enhancements which fall within the scope of the claims which
follow. These claims should be construed to maintain the proper
protection for the embodiments first described.
* * * * *